Field of the Invention
The invention relates to a method for precisely aligning a product to be stapled in relation to a stapling device in a gatherer stapler. The invention also relates to a correspondingly constructed gatherer stapler.
Gatherer staplers are paper-processing machines with which a product, for example a brochure, is assembled from a plurality of folded sheets and is stapled. Printed folded sheets from sheet piles or stacks are supplied separately lying on folded sheet feeders or standing on the spine, are opened and placed on a gathering chain. The number of folded sheets to be stapled is gathered and aligned on the gathering chain by drivers. The gathering chain transports the gathered folded sheets to a stapling device, whereat they are stapled with wire staples by suitable stapling heads. In order to trim the edge of the stapled products, there is usually provided downstream from an ejector, a so-called trimmer from which the end products are transported onward to a delivery.
In gatherer staplers, a distinction is drawn between two types of stapling: stapling at a standstill and stapling while moving.
In order to perform stapling at a standstill, the product must be stopped. A disadvantage thereof is that the product may change its position because of disruptive influences during retardation and acceleration of the movement thereof.
In order to staple the moving product, the stapling device, including a stapling carriage and a staple lifting device, have to be moved together with the product to be stapled and, at least for some time interval, must be coordinated with the movement of the product. The coordination of the movement of the stapling device is carried out, in this regard, in relation to the movement of the gathering chain which transports the product to be stapled. Then, the position of the product is determined by the composition of the gathering chain, more particularly by the composition of the drivers of the gathering chain. In this type of stapling, deviations occur between the actual staple position and the desired staple position, and the deviations may be pronounced to a different extent from product to product. Deviations of the staple position result, amongst others, from the fact that the movement of the stapling device is coordinated with the movement of the gathering chain and, at the same time, it is assumed that the product to be stapled is precisely guided by the gathering chain.
European Patent EP 0 917 965 reveals a gatherer stapler for folded sheets and a method for controlling the drive of a gatherer stapler. The gatherer stapler for folded sheets disclosed therein has a stapling station and at least one folded sheet feeder, a gathering chain and a drive. In order to permit flexible use and operation of the gatherer stapler, the drive comprises individual drive units, of which, respectively, one drive unit is associated with the stapling station, each folded sheet feeder and the gathering chain, and each of the individual drive units has at least one electric motor and at least one control unit associated therewith. Also provided is a connection for the interchange of data and/or control signals between the control units.
Due to tolerances in the length of the gathering chain pitch, due to tolerances and positional deviations of the drivers, and due to tolerances in the chain guide elements, the actual position of the product to be stapled deviates from the expected position in the transport direction.
Heretofore, attempts have been made to minimize the foregoing deficiency by predefining or prescribing close tolerances for the components which are used. Wear phenomena, for example, of the gathering chain, lead to changes in the length of the chain segments with increasing duration of operation. Consequently, the deviation of the staple position is increased.